Enforce import of all submodels in `model.__init__`
Enforce import of all submodels in `model.__init__`

Else, if some parts of the model never have been imported (e.g. when
running the gerok importer script, which does not depend on traffic),
the medatada does not know these parts exist.  Therefore, they won't
be included on `metadata.create_all`.

lukasjuhrich/pycroft,agdsn/pycroft,agdsn/pycroft,lukasjuhrich/pycroft,lukasjuhrich/pycroft,lukasjuhrich/pycroft,agdsn/pycroft,agdsn/pycroft,agdsn/pycroft